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Surge protection

Discussion in 'Electronic Basics' started by [email protected], Feb 14, 2006.

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  1. Guest

    Hi all,
    I am working on a Engine - compressor based crawler machine.
    having 24v DC system.
    One microcontroller is used on the m/c for measurement of revolutions
    of gear motor.
    Problem:- Due to some 10-12 solenoid valves are also operated from the
    same 24V DC source facing a problem of surges causing failure of
    controller.
    we tried to use diodes & capacitor combination across each solenoid to
    suppress surges still the problem persist.

    Please advise what modification can be done.
     
  2. Maybe a Varisitor? Is the power supply to the microcontrollers regulated?


    A quick search in google returned

    http://focus.ti.com/lit/an/slup100/slup100.pdf
     
  3. Dan Hollands

    Dan Hollands Guest

    To suppress a coil operated from dc, a reverse diode across the coil with no
    capacitor is usually all that is required.

    When faced with this type of problem the whole system needs to be reviewed
    for ways that the noise is getting to the ucontroller.
    including wire routing, location of parts, filtering of power supply,
    filtering on the ucontroller board, filtering of incoming and outgoing
    signals, grounding etc. - this often takes experience and detective work to
    solve. (Solving these problems is one way to gain experience)

    Dan


    --
    Dan Hollands
    1120 S Creek Dr
    Webster NY 14580
    585-872-2606

    www.QuickScoreRace.com
     
  4. Pooh Bear

    Pooh Bear Guest

    I barely know where to start. You've clearly got yourselves into a mess
    through a failure to understand basic good design practice.

    You probably have EMI problems - maybe also 'dirty grounds'. Without a
    detailed knowledge of the product it's hard to say.

    As the Irish would say " If I wanted to get there, I wouldn't start from
    here " !

    Graham
     
  5. Pooh Bear

    Pooh Bear Guest

    Yes.

    In short you need an expert. Something that was likely missing from the original
    design team.

    Graham
     
  6. ehsjr

    ehsjr Guest

    It might be sags, not surges, if those solenoids draw a lot
    of current. You could feed the 24V through a diode to a
    big cap on the input of the voltage regulator that powers
    the controller. When the solenoids operate, they can't suck
    the charge off the cap due to the diode, so the controller
    Vcc won't see the sag, if it exists.

    Ed
     
  7. Pooh Bear

    Pooh Bear Guest

    It could be *almost anything* given the vagueness of the OP's post.

    One would hope that they have at least used clamp diodes across the solenoid
    coils.

    I think we can safely assume that his uC isn't powered directly from the 24V
    though. Since it'll be powered by some voltage regulator somewhere a good
    question would be to enquire if the regulation is/isn't local and.or whether
    it shares any current paths with the load(s) - look for 'ground noise'.

    I'd also look very closely at trace loop areas to see if there's some
    electromagnetic coupling between the solenoids' magnetic fields and the uC
    inputs.

    Graham
     
  8. Rich Grise

    Rich Grise Guest

    Separate the power leads at the battery, so that the solenoids and
    the uP regulator have separate power/ground loops; optoisolate the
    processor; ideally, use a separate battery for the uP.

    Good Luck!
    Rich
     
  9. Sam Nickaby

    Sam Nickaby Guest

    You mean like this product? http://www.apexi-usa.com/product_electronics_detail.asp?id=224&pageNum=1

    This product looks expensive. But by using an extra isolated
    battery just for the controller would be much more cost effective.
    The question is how to separate the two power source once
    the 10-12 solenoid valves begin to operate? I have about the
    same dilemma as the OP for my car alarm that goes off during
    driving when it's on the same battery as the car.
     
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